Although the use of colored glass is not especially limited, it can be applied for privacy glass or the sun roof of car safety glass and building glass, etc. As compared with general soda-lime glass, colored glass can lower visibility in motor vehicles because of its low visible light transmittance (LTA) and can reduce heat absorption into motor vehicles because of its low solar energy transmittance (Te). In addition, since it has low ultraviolet rays transmittance (Tuv), damage to fabrics and discoloration or decomposition of articles inside motor vehicles due to ultraviolet rays can be prevented.
Various elements can be incorporated into colored glass in order to improve the glass color, UV-blocking effect, and solar energy absorption effect. The representative elements used in colored glass include iron (Fe), cobalt (Co) and selenium (Se), and chromium (Cr), manganese (Mn), titanium (Ti), cerium (Ce), nickel (Ni), copper (Cu), etc. may be further used. Each of these elements has a unique coloring effect, and the absorption characteristics of ultraviolet rays and solar energy. Such characteristics result from the phenomenon that each element absorbs its specific wavelength. Accordingly, the desired color and transmittance may be designed through the combination of added elements in appropriate ratios.
By properly adjusting various elements as explained above, it is possible to prepare a dark, green-gray colored glass composition. Specifically, a glass having high absorbance property of visible light, ultraviolet rays and solar energy (i.e., low transmittance property) can be prepared. Such a low-transmittance glass composition can be divided into two groups, in which one group is prepared by using Fe, Co and Se as basic elements for coloring while the other group further uses additional elements.
U.S. Pat. No. 4,873,206 discloses a glass composition comprising 0.6 to 1.0% by weight of total Fe2O3, 0.005 to 0.02% by weight of Se and 0.01 to 0.02% by weight of CoO, and not containing Ni and Cr. However, this composition has a visible light transmittance (LTA) of about 25 to 30% as measured for a reference thickness of 4 mm and thus is not suitable for providing the function of privacy protection which is an important function of a low-transmittance glass composition applied for sunroof or rear privacy glass. In addition, there is a limitation in preparing a dark, green-gray colored glass composition.